1. Filed of the Invention
The invention relates to a method of making a metallic thin wire in the form of a flexible wire configuration used as a main wire component of a medical tool such as a catheter, a catheter guide wire, an endscope treating instrument or the like.
2. Description of Prior Art
In a catheter and a catheter guide wire which introduces a leading distal end into a diseased area through a sinuous vascular system, the leading distal end of the catheter or the catheter guide wire is inserted into the blood vessel or the somatic cavity by a “push-pull and turn” manipulation at a hand access portion located outside a subject patient upon treating the diseased area. In an endscope treating instrument which is inserted through a somatic cavity to reach the diseased area, a leading end of the endscope treating instrument is manipulated in the same manner as mentioned above.
In order to achieve a smooth manipulation when inserting the leading distal end into the somatic cavity and the blood vessel, it is required for these medical devices to have multi-mechanical properties. The multi-mechanical properties include a high flexibility, a good straightness and restitutivity in an unrestricted free state against bending deformation. The medical devices of these types are required at its leading distal end portion to have a high flexibility, while at the same time, required at its rear portion to have an appropriate rigidity as a functionally gradient property. It is also indispensable for the leading distal end to have a good maneuverability in which the leading distal end properly responds to the hand operation conducted outside the subject patient.
The following publications disclose flexible linear wires used as a main component of the medical devices with an aim to achieving the above indispensable multi-mechanical properties.
In the references of Laid-open Japanese Patent Application No. 7-148267 and Domestic Publication No. 2000-512691 (referred in turn to as “first and second reference” hereinafter), the first reference shows a method of making a metallic thin wire in which a metallic wire is mechanically rolled straight through a correction roller, and then thermally treated to remove a residual stress so as to produce a medical guide wire superior in linearity and straightness.
The second reference also shows a method of making a metallic thin wire in which a thin wire is made of a shape-memory alloy, and twisted under a tensile force applied to the thin wire, and then thermally treated to remove a residual stress so as to produce a catheter guide wire.
The medical guide wire produced by the first reference is superior in a lengthwisely directed straightness. It is, however, poor in torsional characteristics. This leads to a shortage of the torque transmissibility and rotational maneuverability so as to reduce a good steerability.
The catheter guide wire produced by the second reference specifies the shape-memory alloy, and only one metallic thin wire is prepared each time the method is used upon producing the catheter guide wire. This makes the catheter guide wire costly and disadvantageous especially when brought to the mass production. In addition, the metallic thin wire is twisted only in one direction, and thus making the torsional characteristics uneven in the lengthwise direction. Because the metallic thin wire is twisted only in one direction, and not twisted further in another direction, the metallic thin wire becomes to lose the torque transmissibility and rotation-following capability so as to reduce the steerability when applied to the medical guide wire, and maneuvered to swivel the guide wire in the right and left directions upon inserting the guide wire into the vascular vessel.
Therefore, it is an object of the invention to overcome the above drawbacks so as to provide a method of making a metallic thin wire for a medical tool which are capable of improving a rotation-following capability and torque transmissiblity so as to enhance a steerability.
According to the present invention, there is provided a method of making a metallic thin wire which is twisted in one direction under a tensile weight applied in the lengthwise direction, or primarily and secondarily twisted alternately in one direction and the opposite direction under the tensile weight applied in the lengthwise direction. This induces a uniform torsional rigidity in the right and left directions through an entire length of the one single metallic thin wire.
According to other aspect of the present invention, one single metallic thin wire is prepared to have a predetermined length or a bifold extension of the predetermined length. A middle portion of the one single metallic thin wire is fixedly supported at a fixed portion. Front and rear half portions of the one single metallic thin wire is twisted (in one direction) with the front and rear half portions symmetrically located at both sides of the fixed portion. At the time of twising the front and rear half portions, a tensile weight is concurrently applied to the front and rear half portions. This produces two metallic thin wires simultaneously in a dual-way fashion to maintain the product quality uniform, while at the same time, improving the productivity.
According to other aspect of the present invention, the one single metallic thin wire which is primarily twisted is further twisted secondarily. At the time of primarily twisting the one single metallic thin wire, the one single metallic thin wire is excessively twisted nearly to induce slip lines (Lüder's lines) on an outer surface of the one single metallic thin wire. Total turning times of the secondarily twisting step is more than 0.15 times of that of the primarily twisting step, but less than 1.5 times of that of the primarily twisting step. It is preferable that the primarily twisting numbers of times is 0.2 times as great as that of the secondarily twisting numbers of times.
The one single metallic thin wire is divided into a plurality of zones in the lengthwise direction, each of which is twisted in different number of turns, or processed with the heat treatment in varied degrees so as to enhance the performance when the one single metallic thin wire is applied to a medical tool or equipment. From the same viewpoint, an outer surface of the one single metallic thin wire is treated with an electrolytic polishing procedure. Alternatively, the one single metallic thin wire is made of an austenitic stainless steel.
The metallic thin wire thus produced is applied to a main wire element, a shaft, a stylus, a pull-wire, a stent and a needle in the medical tools such as, for example, a catheter, a balloon catheter and a medical endscope.
From the viewpoint of an operation and advantages of the present invention, the one single metallic thin wire is twisted in one direction or primarily and secondarily twisted alternately under the lengthwise tensile weight. This reduces a torsional elasticity to impart the one single metallic thin wire with an enhanced torsional rigidity. When the one single metallic thin wire is primarily and secondarily twisted alternately, the uniform torsional rigidity develops in the right and left directions through an entire length of the one single metallic thin wire.
By primarily twisting the one single metallic thin wire excessively beyond the yield point, a slipping stress prevails through the entire length to induce wavy slip lines (Lüider's lines) on the weak portion of the one single metallic thin wire so as to equalize the torsional characteristics through the entire length of the one single metallic thin wire. By secondarily twisting the one single metallic thin wire after primarily twisted, the excessive amount of the twisted turns is retrieved to a certain degree, and then the one single metallic thin wire is processed with the heat treatment to remove the residual stress. This imparts the metallic thin wire with a highly improved linearity and straightness.
When the one single metallic thin wire is processed with the heat treatment while excessively twisted only in one direction, the one single metallic thin wire is likely to torsionally and wavily deform due to the reaction force developed from excessively twisting the one single metallic thin wire.
When the one single metallic thin wire is processed with the heat treatment while not excessively twisted in one direction, the one single metallic thin wire is likely to become bendable, although the heat treatment decreases the torsional and wavy deformation, to which the one single metallic thin wire is subjected.
In general, the one single metallic thin wire has a tendency to develop the torsional and wavy deformation due to an uneveness between one portion in which an elastic reaction develops against the torsional direction and other portion in which a plastic deformation starts to appear when the one single metallic thin wire is twisted with one end of the thin wire as a fixed portion.
In the present invention, the one single metallic thin wire is primarily and secondarily twisted alternately in mutually opposed directions. This makes the resultant numbers of twisting turns uniform with a high torsional rigidity due to a total sum of the twisting turns in the right and left directions when taking the primarily and secondarily twising numbers plus and minus respectively.
The one single metallic thin wire is primarily and secondarily twisted alternately under the tensile weight applied to the one single metallic thin wire, and then processed with the heat treatment to remove the residual stress.
This produces the metallic thin wire highly superior in the rotation-following capability (torsional rigidity and torque transmissibility) in both the right and left directions while securing a high flexibility and linearity in the one single metallic thin wire.
For a medical tool and equipment into which the metallic thin wire is incorporated as the main wire component, the present method enables the main wire component to a highly superior rotation-following capability (torsional rigidity and torque transmissibility) so as to enhance the performance depending on its usage.